Question regarding flue temp

[cricco]

Hi all. I have a simple question that I cannot find an answer for. My Newmac Oil/Wood boiler is connected to a 35 foot Selkirk Stainless chimney via a 4 foot length of single wall black stove pipe 8" in diameter. I have blocked off my barometric damper to eliminate creosote buildup, which seems to be working. I have a magnetic thermometer attached to the single wall pipe just before the connection to the Selkirk chimney. The temperature usually runs around 250 degrees. I try to get a really ripping fire once a day by opening the ash door until the fire gets really blazing. This will get the temp up to 350-400 degrees. Folks keep saying that a normal temp is 500-800 degrees, and I just can't believe this is correct! With my boiler blazing like a blast furnace, I'm lucky to hit 450 degrees. Am I doing something wrong, or is my flue temp OK? What temp should I be at??

 

[mikeyny]

I have an older tarm, the book says I should have a max stack temp of 6oo to 750. I had too much draft and managed to slow it down to 500. I also use a magnetic therm. I have heard they are not very accurate and a flue gas temp gauge should be inserted into the smoke pipe for more accurate readings. If you have too much creosote your stack temps will be down. Most of us seasoned wood burners determine the condition of our chimneys by the max stack temp. As the seasons progresses and the max stack temp lowers it means it is time to clean your chimney or risk having a chimney fire. And then again some of us get our chimneys cleaned by having a good old chimney fire. Thats a little too riskey for me though.

 

[rwh442]

I am not 100% positive on this but I believe the magnetic type stack thermometers read quite a bit lower than actual internal temperatures. For some reason 1/2 the temp seems to be what I have heard. So your 250 degrees may be near 500 internal. Hope someone else chimes in to confirm.

I played around with stack temperatures all last year with my boiler and found out that it likes to run around 600 degrees interna stack temperaturel for a much cleaner burn.

Try purchasing an internal type temperature probe for confirmation.

 

[Singed Eyebrows]

Hi all. I have a simple question that I cannot find an answer for. My Newmac Oil/Wood boiler is connected to a 35 foot Selkirk Stainless chimney via a 4 foot length of single wall black stove pipe 8" in diameter. I have blocked off my barometric damper to eliminate creosote buildup, which seems to be working. I have a magnetic thermometer attached to the single wall pipe just before the connection to the Selkirk chimney. The temperature usually runs around 250 degrees. I try to get a really ripping fire once a day by opening the ash door until the fire gets really blazing. This will get the temp up to 350-400 degrees. Folks keep saying that a normal temp is 500-800 degrees, and I just can't believe this is correct! With my boiler blazing like a blast furnace, I'm lucky to hit 450 degrees. Am I doing something wrong, or is my flue temp OK? What temp should I be at??

I was told by boiler engineers that internal flue gas temps(center of pipe) are normally double what a magnetic thermometer will read. Your usual 250 sounds good to me as this should be actual 500 internal. The "folks" probably mean internal temps, Randy

 

[ohbie1]

[I was told by boiler engineers that internal flue gas temps(center of pipe) are normally double what a magnetic thermometer will read. Your usual 250 sounds good to me as this should be actual 500 internal. The "folks" probably mean internal temps, Randy

My experience supports what Randy says. I have a magnetic and a probe. The probe consistently reads 2X the magnetic, give or take 20 degrees.

 

[cricco]

Well, I took the advice of the board members. I'm impressed! I purchased a probe thermometer and the results are surprising. My magnetic Rutland thermometer reads 200 deg, and the probe reads 600 deg! So, I guess my stack temps are fine. I couldn't believe what a difference there was in temperature readings! Throw those magnetic thermometers away!!

 

[LeonMSPT]

I burn coal mostly, sometimes wood, and have magnetic thermometers... that they're not "exact" as a probe type thermometer should not come as a shock to anyone. The thing is stuck on the outside of the metal pipe, the probe is inside the stream of gasses moving through it. As creosote builds up on the inside of the pipe it insulates the pipe and reduces the temperature on the thermometer.

I do have to question the "double it" theory however... really?

When I've got a good bed of coal purring away approaching maximum temp and can actually watch the boiler temperature needle moving upward... the mag therm on the door says 425 and the stack temp says 475... Double? Seems like all I'd be brushing out of the pipe weekly is a little dust if I was hitting those temps, and the walls of my firebox would be much cleaner than they are...

I'll buy a probe type and check it out though... interesting.

Watch out, blocking barometric dampers... my boiler's manual was specific and in numerous places advised to limit the draft on the boiler to less than .04 inches of water. Stack temps can go too high overdrafting the boiler, and it won't burn efficiently if it's trying to combust in a vacuum. Mine was puffing back at me, and was getting frequent coal gas explosions until I put the barometric damper BD, in and adjusted it to .02 inches of draft. Was also loading the thing every 3-4 hours on coal, and 2-3 hours on wood... the smoke was awful under those conditions. Stack temps on the mag therms was running 475-600 degrees... too hot. With the conditions lacking the BD, it was not a matter of "if" I was going to have a chimney fire, but "when".

Well, I took the advice of the board members. I'm impressed! I purchased a probe thermometer and the results are surprising. My magnetic Rutland thermometer reads 200 deg, and the probe reads 600 deg! So, I guess my stack temps are fine. I couldn't believe what a difference there was in temperature readings! Throw those magnetic thermometers away!!

 

[Singed Eyebrows]

I burn coal mostly, sometimes wood, and have magnetic thermometers... that they're not "exact" as a probe type thermometer should not come as a shock to anyone. The thing is stuck on the outside of the metal pipe, the probe is inside the stream of gasses moving through it. As creosote builds up on the inside of the pipe it insulates the pipe and reduces the temperature on the thermometer.

I do have to question the "double it" theory however... really?

When I've got a good bed of coal purring away approaching maximum temp and can actually watch the boiler temperature needle moving upward... the mag therm on the door says 425 and the stack temp says 475... Double? Seems like all I'd be brushing out of the pipe weekly is a little dust if I was hitting those temps, and the walls of my firebox would be much cleaner than they are...

I'll buy a probe type and check it out though... interesting.

Watch out, blocking barometric dampers... my boiler's manual was specific and in numerous places advised to limit the draft on the boiler to less than .04 inches of water. Stack temps can go too high overdrafting the boiler, and it won't burn efficiently if it's trying to combust in a vacuum. Mine was puffing back at me, and was getting frequent coal gas explosions until I put the barometric damper BD, in and adjusted it to .02 inches of draft. Was also loading the thing every 3-4 hours on coal, and 2-3 hours on wood... the smoke was awful under those conditions. Stack temps on the mag therms was running 475-600 degrees... too hot. With the conditions lacking the BD, it was not a matter of "if" I was going to have a chimney fire, but "when". That is good advice, to not second guess the manufacturer of your boiler etc. My Atmos requires .1 WC draft & I have this with a strong drafting chimney, Randy

Well, I took the advice of the board members. I'm impressed! I purchased a probe thermometer and the results are surprising. My magnetic Rutland thermometer reads 200 deg, and the probe reads 600 deg! So, I guess my stack temps are fine. I couldn't believe what a difference there was in temperature readings! Throw those magnetic thermometers away!!